1. Field of the Invention
The present invention relates to a calculator comprising a display for displaying an inputted numerical formula (hereinafter described as "inputted formula"), for calculating the numerical formula and for displaying the results according to the key operation of a user.
2. Description of the Related Art
Hitherto, electronic desktop calculators (hereinafter described as "calculators") having various functions have been presented. The calculator disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. JP-A 2-176849 (1990) is provided with first and second displays, and operates every time a numerical value is entered and a function key is pressed. The result of the operation is displayed in the first display, and the previous operation result in the second display. Thus, the previous operation result is shown in the second display on every key input, so that the user can proceed with the operation while easily confirming the intermediate result of operation.
The display apparatus of the calculator disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. JP-A 4-297948 (1992) is provided with four displays, namely, a first-operand display, a second-operand display, an operation result display, and an operator display. For example, by an input of "12+36=" by continuous key input operations, it is constituted so that "12" may be displayed in the first-operand display, "+" in the operator display, "36" in the second-operand display, and "48" in the operation result display, and all the key-inputted values in the process of operation are displayed at the same time, so that the user of the calculator can visually confirm with ease.
In the data display apparatus disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. JP-A 48-24639 (1973), a television receiver capable of displaying an image in plural lines while scanning is utilized as a display apparatus of a calculator, and when a key input of, for example, "12.times.4=" is entered, "12" displayed in the first line, ".times.4" in the second line, and "48" in the third line of the receiver sequentially, and a parting line is shown between the second and third lines, so that the process of operation is displayed by clearly distinguishing between the operands and the operation result.
The prior art disclosed in the above publications is merely intended to show the key input values or the operation result value in the corresponding display area out of plural display areas for individually predetermined applications every time a key input is made for operation, and the problem is that it is not constituted to display the processes of operation (including conversion of value and transformation of formula) from the input operation formula till finding the answer. Hence, it is disadvantageous that, for example, a schoolchild cannot learn the solution of a formula while confirming every step of the progress of the operation in self-teaching of mathematics.
In some of the conventional calculators, fractions can be calculated, and by inputting a fraction formula, the result of calculation is displayed in a fraction. In such calculator, for example, when a fraction formula "3/6+4/12" is entered in a specified method from the keyboard, a calculation result "5/6" is shown in a display.
Although fractions can be calculated in certain conventional calculators, what is displayed is only a calculation result for an inputted fraction formula.
In recent school education, calculators capable of calculating fractions have come to be employed. In such a case, although it is important to know the calculation result of the fractions, it is more important from the educational aspect to know the process of finding the result of calculation. In the conventional calculators, however, the calculation process of fraction formulas cannot be known, which is a problem from the educational point of view.